1. Field of the Invention
The present invention relates generally to bulk handling apparatus and in particular to storage apparatus for storing bulk granular materials.
2. Discussion of the Prior Art
Bulk granular materials are typically stored in silos or large sheds. Silos are mostly utilized for storing grain and reclaiming is achieved through a base cone arranged coincident with the repose angle of the grain such that all material will feed gravitationally to a central outlet for discharge from the silo. A disadvantage of this arrangement is that such silos are relatively high and this necessitates additional cost and complexity for equipment to feed grain into the silos.
Mined bulk granular material is often stored in sheds where it may be deposited, for example, by a central conveyor supported in the apex of a conventional portal frame shed. Reclaiming of the product is achieved using front end loaders charging dump hoppers travelling over an out-load conveyor which may be arranged in a tunnel and fed from a central point. Capital costs of such designs are very high and large land areas are required for such storage. Additionally, there is an ongoing reclaim cost necessitated by the use of supervised machinery to reclaim the material from the shed.
A further disadvantage of these systems is that many bulk solids have properties that will allow the forming of rat-holing and make those materials bridge over an out-loading point thereby stopping the exit flow of materials. The problem of bridging and rat-holing may become extreme in cases where material has been in static storage for a considerable period of time thereby having allowed gravitational pressures to cause settlement or compaction of what may have been a relatively freeflowing material.
Hydroscopic properties of some materials will allow them to become sticky in storage adding further to the problems of extracting such materials from silo type storage. Mined bulk granular material is also stored as open stockpiles serviced by rail mounted stacker reclaiming machinery. Disadvantages of such systems include the high cost of stockpiling and management with regard to the environment and high maintenance costs of the necessary equipment for stockpiling and reclaiming.
The present invention aims to alleviate at least one of the above disadvantages and to provide storage apparatus which will be reliable and efficient in use.
With the foregoing and other objects in view, this invention in one aspect resides broadly in storage apparatus suitable for storing granular material. The storage apparatus includes a storage container, a material inlet at the top of the storage container, a material outlet at the base of the storage container, and a height adjustable leveling apparatus for leveling the upper surface of material contained in the storage container. Thus the upper surface may be levelled to enable the container to be filled to capacity when filling, and when discharging to level the upper surface to ensure complete discharge of all materials as the container is emptied from the base.
The leveling apparatus could be any suitable form of conveying apparatus which conveys the material being fed into the container towards the outside of the container when filling and when emptying which conveys the material remaining about the periphery of the container towards the center of gravitational; discharge at the base.
In a preferred embodiment, the leveling apparatus is in the form of a driven rotary scraper rotatable about a vertical axis and having an overall diameter substantially equal to the inside diameter of the container, the scraper having blades thereon engagable with the upper surface of material in the container so as to move the engaged material selectively inward or outward as required. For this purpose, the blades may be fixed or adjustable and the wheel may be reversible to control the direction of feed of the granular material.
Alternatively, the vanes may be reversible or the scraper may include alternate sets which may be lowered for engagement with the granular material. Preferably the rotary scraper includes an outer ring frame supported on vertically adjustable mountings on or adjacent the container wall. It is also preferred that for the best mechanical advantage, the drive apparatus for selectively rotating the wheel are mounted on the vertically adjustable mountings and drive the outer ring frame. The drive motor may drive a pinion engaged with an annular rack on the ring frame. Alternatively, the rotary scraper may be supported from a central column and drive therefrom. However this would impose complexities and high loads due to the need to transmit high operating torque through the column to an inner ring of the rotary scraper.
This invention may also be applied to reclaiming materials from an unsupported pile. Thus according to another aspect this invention resides broadly in a method of and apparatus for reclaiming material from a stockpile of granular material including: providing a height adjustable spreading apparatus for spreading material from the upper surface of the stockpile outwardly for passage to the base of the stockpile; providing reclaiming apparatus at the base of the stockpile, and operating the spreading apparatus to cause feeding of that material in the stockpile which does not initially flow gravitationally to the reclaiming apparatus toward the base of the remaining stockpile to enable feeding of substantially all the material in the stockpile reclaiming apparatus. The stockpile may be supported on a base pad containing the reclaiming apparatus and, if desired, the stockpile may be contained within a peripheral wall. In a further aspect this invention may utilize open stockpile arrangements suitable for storing and or blending granular bulk solids and including: a circular storage or blending area; material outlet port or ports positioned on the storage area centerline at the base of the storage area; peripherally positioned supporting towers providing support for the height adjustable leveling-reclaiming apparatus; a centrally positioned support column and distribution means and the leveling apparatus generally as described earlier, may be supported in a peripheral annular support truss, this support truss in turn may be supported via the provision of a series of cabled sheaves and counterweights arrangements at the peripheral support towers.
The counterweight and cable and sheave system will be arranged to create a balance of mass between the leveling apparatus and the counterweights. Such a design requires only limited force to promote the up or down movement of the leveling/reclaiming apparatus The design of the counterweight sheave system will ensure that limited travel of the counterweights will enable the leveling apparatus to traverse the full operational height of the stockpile.
The leveling apparatus may then be directed up or down by simple mechanical means positioned at the base of each of the support towers. When applying the foregoing to a very large diameter stockpile additional support for the leveling apparatus may be provided at the inner hub of the leveling apparatus.
An inner annular truss providing support to the leveling apparatus may be counter balanced by a cable sheave and counterweight arrangement housed inside the hollow center support column. A single mechanical raising and lowering arrangement such as for instance a hydraulic ram may be selected to effect the required up and down travel of the leveling apparatus.
The leveling apparatus in the open stockpile application suitably has the scraper blades positioned in such a way so as to have the blades on the underside of the inner section of the leveling apparatus scrape the material outward to a position coincident with the top of the repose angle of the material stored. The rest of the scraper blades on the outer section of the leveling apparatus are positioned opposite to provide the outer part of the apparatus with inward scraping blades. These scraper blade positions ensure that the stockpile can be totally reclaimed of all stockpiled material. It follows that the reclaim ports should be positioned under the stockpile coincident with a position vertically down from the top of the repose angle at the top of the stockpile.
Driving of the leveling apparatus in the open application may be by means of a friction drive as described earlier but with the motor/gearbox or hydraulic drive pack drive units positioned at three equi-spaced points at the periphery on the leveling-reclaiming apparatus and having electric power supplied via a slipring arrangement at the center hub. Actual friction drive power is suitably applied at the outer annular support truss, this support truss is slideably attached to the perimeter support towers and supported by a series of counterweights inside the support tower structures. The support towers serve as the reaction columns for the drivers.
Operation of the leveling apparatus may be determined so as to have the apparatus, while the stockpile is in charging mode, rotating at its top position this will allow the incoming material to form a pile around the center column. This pile is embraced by the angle of repose of the material stored.
With only the material at the top of the pile being bladed outward, different grades of material may be added to the stockpile thus forming within the parameters of the installation an ever widening frustum pile consisting of several grades of material. Materials may be added to the stockpile until the base area of the stockpile is fully utilized. Reclaiming action of the leveling apparatus will reclaim layers of the varying grades of material, while in the process, blending the different grades into a new homogenous material composed of percentages of the grades that make up the stockpile.
The open stockpile management system may of course be enclosed with a lightweight low cost metal clad type structure providing weather or environmental protection should this at any time become necessary or desirable.
The reclaiming method and apparatus of this invention may be used to advantage with conventional silos and constitutes a further invention.